I'm going to channel Scottsdale...
As a brand-new owner of a 2.13 GHz MBA, I have to say that the MBA is already a great machine. The only thing it's missing IMHO is 4GB of RAM, and that's only a serious limitation if you're planning to virtualize Windows, in which case you're probably a better candidate for a MacBook Pro.
For everyday computing, the MacBook Air is a very fast machine. The only area where it doesn't compete with my 8-core Mac Pro is compute-intensive tasks. And that's why I have the Mac Pro.
If you're a power user and you want one machine to do it all, the MacBook Air is not the right tool for you. In all other cases, the MacBook Air is already a great machine.
My $0.02.